92 GMC Air Conditioner Blows Cold/Warm Intermittently

My 1992 GMC Sierra ext. cab p/u has an a/c problem. When it is first started for the day (in the morning), it blows very cold air. I have a 14 mile drive to work and it stays cool the entire trip.

At lunch, the a/c stays cool for about 3-4 minutes, then it starts to get warm and gets a musty smell. If I accelerate heavily, the cool air starts to come back, but when I let off the accelerator, the air gets warm again. It kind of jumps back and forth between cool and warm and will eventually go completely warm. If I turn off the a/c for about 10 minutes, it is cool again but only for a while.

About two years ago I replaced the pressure switch (?) that is by the evaporater (?) next to the firewall. I am not a mechanic so I'm not sure my terminology is correct. The "evaporater" is what looks like an aluminum can. The switch connects to the side of this can.

I did notice before the warm air thing started that the compressor seemed to be cycling on and off pretty frequently. It would kick on for about 2-3 seconds, then go off for about 5-6 seconds. BTW, this is an R12 system. I have a friend who works for an auto parts store who has access to the necessary equipment to convert it to R134 if we have to. Does anyone know if this can be done without replacing a bunch of a/c parts?

It has been this was all season (since May). It is now in the upper

90's and we will soon be over 100 when August rolls around. I would like to get this figured out before it gets outrageously hot.

Thanks.

Reply to
Steve Lockridge
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The aluminum can is probably the accumulator/drier.

This sound like low refrigerant.

Reply to
Mike Walsh

How is your engine temperature? Your engine may be getting hot enough that it is flipping the thermo protection switch and turning the A/C compressor off, trying to protect itself from overheating. I had a similar problem and found it to be the thermostat. Could be something that simple, but you need to find out your real engine temp.

Scott

Reply to
Scott Fuhrman

Somewhere in the A/C system is (or should be) a "sight glass", probably on the receiver/dryer. It isn't much larger than a pencil eraser. If you can find it, do you see bubbles inside when it's on? If so, you need more refrigerant. A service manual at your local library would probably have this info (on where to find it, if it even has one)

Reply to
Bob M.

The engine temp is normal, although I don't know exactly what normal is because each mark on the temp gauge isn't labeled. It's usually a couple of marks below 210° which I would assume is around 180-190°. I replaced the thermostat a couple of years ago because it stuck open.

Thanks for your help. This has been a confusing problem. I think I might try replacing the cycling switch again and see if that does anything. With it being intermittent, it is almost like some electrical part is getting hot and won't come on or, something is getting cold and freezing up temporarily.

Steve Lockridge snipped-for-privacy@websitewarehouse.com

Reply to
Steve Lockridge

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